The organic compounds undergoing a reversible change of color on exposure to photic or thermal energy which are typical and best known are spiropyran derivatives and G. H. Brown: Photochromism (John Wiley & Sons, Inc., 1971), for one, can be consulted for a specific listing of such derivatives and their physical properties.
However, when an attempt is made to exploit the hitherto-known spiropyran derivatives commercially, for example as photo-responsive materials, they are found to present serious problems. Thus, because the meta-stable species (ring opened isomers) are lacking in thermal stability in solutions as well as in polymeric binders, they tend to promptly revert to the ground state or fade out so that the chromic response at a necessary level cannot be sustained for a sufficient duration.
The object of the present invention is to provide a novel compound suited for use in thermochromic and photochromic materials.